1. Field of the Invention
The present invention relates to a video signal processing method to obtain a pixel signal from an input video signal and, more particularly, to a video signal processing method to obtain a pixel signal by sampling an input video signal which consists of a plurality of horizontal scanning lines, such as a television signal and the like.
In addition, the present invention relates to a video recording system for recording an image picture in accordance with that video signal.
2. Description of the Prior Art
Conventionally, when a hard copy is taken from a video signal such as a TV image picture, a graphic display or the like, the pixel (picture element) constitution ratio is determined so as not to cause the distortion in height and width. For example in an NTSC standard television signal, since the number of horizontal scanning lines of one frame is 525 in the interlaced scanning and the number of effective pixels in the vertical direction is about 480, when the height to width ratio is set into 3:4, one picture plane in the horizontal direction is constituted by 640 pixels.
Therefore, in case of expressing the intermediate gradient in dependence upon a size of a dot by forming one dot for one pixel, unless the dots are arranged with a density of at least 6 dots/mm or more, an image picture will become rough, so that an image picture having satisfactory high picture quality cannot be obtained. A size of the image picture at this time is about 8.times.10.7 cm and this size is too small to constitute a picture plane. Therefore, to obtain a large image picture, it is considered a method of making additional pixel data between the sampled pixels using a mathematical interpolating method; however, this method causes the resolution power of the image picture to deteriorate, resulting in a dimmed image picture.
In addition, it is considered a method of increasing the number of sample pixels by raising the sampling frequency, but it is impossible to increase the number of sample pixels since the number of sample pixels in the vertical direction of a picture plane is limited by the number of horizontal scanning lines of the input video signal.
On one hand, in video signal recording systems for recording the sampled video signal, most of them generally sample the video signal consisting of a plurality of horizontal scanning lines in the direction perpendicular to the horizontal scanning direction of such video signal, thereby printing out. In case of performing the printout in such a form, since the main scanning width of the printer corresponds to the number of horizontal scanning lines, the video signal must be recorded by shortening a length of the main scanning line to reduce the image picture.
This point will be described with reference to the drawings. FIG. 1A shows a CRT screen by a video signal, in which H1, H2, . . . are horizontal scanning lines. The sampling is done with sample lines V1, V2, . . . which are almost perpendicular to these horizontal scanning lines. FIG. 1B shows a picture plane formed by a printer, in which A denotes a picture plane of the normal size; B is a picture plane of the reduced size; L is a length of the main scanning line of the printer; and S indicates the main scanning direction.
Although the signals V1, V2, . . . obtained are recorded along the main scanning direction S, since the main scanning length corresponds to the number of horizontal scanning lines, they must be recorded by shortening the main scanning length to obtain the reduced picture plane B.
This method results in waste of time corresponding to only the distance of L--L' for the printer since it is not easy to change the constitution of the printer so as to scan the distance L' in spite of the fact that the printer can inherently perform the main scanning for only L. In addition, since the main scanning distance becomes short, a part of the sampled pixels of only the number corresponding to the number of horizontal scanning lines has to be deleted through thinning-out, or the interpolation processing must be carried out, so that picture quality deteriorates and at the same time a complicated processor has to be used.
In addition, in the case where the multiplying ratio of the number of recording pixels to the number of original pixels in the main scanning direction or the sub-scanning direction of the recording means is represented by N (where, N is a positive integer), for example as shown in Japanese Utility Model Publication Laid-Open No. 27590/83, the same original pixel may be used as the recording pixel N times in the main scanning and sub-scanning directions. On the other hand, when the above-mentioned multiplying ratio is represented by 1/N, only one pixel among the N original pixels may be used as the recording pixel.
However, if the above multiplying ratio cannot be represented by N or 1/N, etc., it is impossible to use the original pixel as it is as the recording pixel, so that a special operation such as the division or the like will be needed. Thus, a complicated circuit is necessary to realize this special operation.